This is primarily an investigation of two important regulatory processes in the replication of paramyxoviruses. One of these is the mechanism that determines the relative rates of synthesis of virus messenger RNA (transcription) versus virus genomic RNA (replication). The other is the mechanism that specifies the abundance of each virus-specified polypeptide in infected cells. These mechanisms will be studied in infected cells by use of inhibitors of RNA and protein synthesis, and in cell-free systems using biochemical methods to identify and characterize the relevant functional macromolecules. Temperature-sensitive mutants defective in these functions will be used to relate in vitro to in vivo events. Another goal is to explore the structure of the paramyxovirus genome, using virus messenger RNA species and subgenomic RNA species derived from defective-interfering virus particles. Methods will include RNA hybridization and electron microscopy.